The invention concerns a method for filling tubes in a tube-filling machine, wherein the tubes are directed to a filling station of the tube-filling machine, and, in the filling station, a liquid or highly viscous product is poured into the tubes by means of a filling apparatus, wherein, after being filled, each tube is weighed and the actual weight is compared with a desired weight, the filling apparatus being adjusted if the variance between the actual weight and the desired weight lies outside predetermined limits.
The invention also relates to an apparatus for filling tubes in a tube-filling machine, with a filling station, in which a liquid or a highly viscous product can be poured into the tubes by means of a filling apparatus.
A tube-filling machine of the conventional type has an endlessly circulating conveying apparatus that comprises multiple holders, into each of which a tube holder is inserted. Each tube holder can accommodate one tube with its head or cap section, wherein each tube together with the tube holder passes through the individual workstations of the tube-filling machine. In a filling station, a product, usually a liquid or highly viscous product, is poured into the tube, which is open at the top, whereupon the tube is sealed, for example, welded, at its upper end in a downstream sealing station and subsequently removed from the tube-filling machine.
The quantity of the product to be poured in is usually dosed volumetrically, i.e. the volume of the product to be poured in is suctioned from a supply container by means of a dosing piston and subsequently pressed into the tube. The filling volume is consequently defined by the diameter of the dosing piston and its travel. However, in practice, it has been shown that this volumetric dosing has disadvantages. In particular, air pockets can become trapped in the filling volume which results in too small a quantity of the product being poured into the tube. Furthermore, the filling volume is subject to fluctuations due to ambient conditions and the composition of the product.
The filling plant of the product or the producer of the filled tubes must guarantee to the customer that the product in the tube complies with a minimum weight. For that reason the weight of the filled tubes is inspected. Once the tubes have been sealed at the upper or lower end and have been removed from the tube-filling machine at the removal station, they move across a weigh-belt on which the weight of each tube is determined. Those tubes that do not comply with a predetermined desired weight are rejected as “bad tubes” and cannot be reused. To keep the proportion of “bad tubes” as low as possible, a known method is to fill the tubes with a volume of the product that is above the desired volume. The disadvantage of this method, however, is that a disproportionally large quantity of the product is poured into the tube, which is uneconomical. Once a sufficiently large number, usually 100, tubes have been weighed, an average value is calculated from the measured values and used as the basis for adjusting the dosing cylinder of the filling station. A disadvantage of this method is that a relatively large number of tubes may have been filled before adjustment of the filling station is corrected. This results in a relatively large number of tubes being imprecisely filled, which then have to be removed from the subsequent production process.
GB 1,012,072 discloses that the process of filling the tube can be controlled by the weight. The tube is positioned on a weighing apparatus during filling and the product is poured into the tube until the desired weight is ascertained by the weighing apparatus, whereupon feeding of the product into the tube is interrupted. However, this method takes a relatively long time to fill the tube with great precision, i.e. filling is relatively slow, which reduces the efficiency of the tube-filling machine.
The object of the invention is to provide a method for filling the tubes in a tube-filling machine, with which the tubes can be filled quickly and with high precision. Moreover, an apparatus for filling tubes in a tube-filling machine is to be provided with which the method can be performed in a simple manner.